Transparent Display Apparatus and Method for Controlling the Same

ABSTRACT

There are provided a transparent display apparatus and a method for controlling the same. The transparent display apparatus includes a transparent display unit that includes an emissive area and a transmissive area and is configured to display a video, an optical sensor configured to measure the amount of light, and a light shielding unit that is disposed on one surface of the transparent display unit and is configured to adjust transmittance on the basis of the amount of light.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/140,184 filed on Dec. 24, 2013, which claims priority from KoreanPatent Application No. 10-2012-0157791 filed on Dec. 31, 2012 in theKorean Intellectual Property Office, both of which are incorporatedherein by reference in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a transparent display apparatus and amethod for controlling the same, and more particularly, to a transparentdisplay apparatus and a method for controlling the same with which it ispossible to improve visibility by shielding incident light on the basisof an analysis of an ambient environment of the transparent displayapparatus.

2. Description of the Related Art

A transparent display apparatus is a display apparatus in which abackground of a screen is transparently seen, and the transparentdisplay apparatus is primarily realized by projecting a video on atransparent screen in the past. However, there has been currentlydeveloped a display apparatus that directly includes a transparentdisplay device. Since a liquid-crystal display (LCD) uses two polarizingplates, the liquid-crystal display has low transmittance, so that it isdifficult to be used as a transparent display apparatus. The transparentdisplay apparatus is mostly realized in an organic light-emittingdisplay device (OLED) capable of self-emitting, especially. Such atransparent display apparatus is applied to a front glass for a vehicleor a glass for home to provide desired information to a user.

SUMMARY OF THE INVENTION

Embodiments of the present disclosure relate to a transparent displayapparatus having a transmittance that is adjusted as external lightincident on the display changes. In one embodiment, the transparentdisplay apparatus comprises a transparent display unit having lightemitting pixel elements and transmitting at least a portion of firstlight incident on the transparent display apparatus. At least one sensorgenerates at least one signal indicative of brightness of second lightincident on the transparent display apparatus. The portion of the firstlight transmitted through the transparent display unit is adjustablebased on the signal indicative of the brightness of the second light.

In one embodiment, the transparent display apparatus includes a lightcontrol unit overlapping with the transparent display unit. The lightcontrol unit has an adjustable transmittance for the first light and canadjust an amount of the portion of the first light transmitted throughthe transparent display unit by adjusting the adjustable transmittanceof the light control unit based on the signal indicative of thebrightness of the second light.

In one embodiment the first light is the same as the second light. Forexample, both the first and second light may be from an external lightlocated at a back surface of the display apparatus. In anotherembodiment, the first light and the second light may be different andare incident on opposite surfaces of the transparent display apparatus.

In one embodiment the at least one sensor comprises a plurality ofsensors that generate a plurality of signals indicative of thebrightness of the second light at different positions of the transparentdisplay apparatus, and the adjustable transmittance of the light controlunit is adjustable in different areas corresponding to the differentpositions of the transparent display apparatus based on the plurality ofsignals.

In one embodiment, the at least one sensor also measures a proximitybetween the transparent display apparatus and an external object, andthe portion of the first light transmitted through the transparentdisplay unit is further adjustable based on the proximity. In oneembodiment, the at least one sensor comprises an image sensor.

In one embodiment, the portion of the first light transmitted throughthe transparent display unit is further adjustable based on a targetcontrast ratio of the transparent display apparatus. Additionally, theportion of the first light transmitted through the transparent displayunit may be further adjustable based on a maximum luminance of the lightemitting pixel elements.

In one embodiment, the portion of the first light transmitted throughthe transparent display unit is decreased as the brightness of thesecond light increases. In one embodiment, the portion of the firstlight transmitted through the transparent display unit is adjusted to amaximum amount when the brightness of the second light is equal to orless than a first reference brightness value, and the portion of thefirst light transmitted through the transparent display unit is adjustedto a minimum amount when the brightness of the second light is equal toor greater than a second reference brightness value.

In one embodiment, the transparent display apparatus supports at least afirst mode, a second mode and a third mode of operation. In the firstmode, the portion of the first light transmitted through the transparentdisplay unit is maximized. In the second mode, the portion of the lighttransmitted through the transparent display unit is minimized. In thethird mode, the portion of the first light transmitted through thetransparent display unit is adjustable based on the signal indicative ofthe brightness of the second light.

In one embodiment, a maximum luminance of the light emissive pixelelements is adjustable based on the signal indicative of the brightnessof the second light. For example, a gamma voltage to the transparentdisplay unit may be adjustable to adjust the maximum luminance of thelight emissive pixel elements.

In one embodiment, the portion of the first light transmitted throughthe transparent display unit is maintained constant when the brightnessof the second light changes more than a predetermined number of times ina predetermined period.

In one embodiment, a method of operation in the transparent displayapparatus is disclosed. The method comprises generating at least onesignal indicative of brightness of the external light incident on thetransparent display apparatus; and adjusting the portion of the externallight transmitted through the transparent display unit based on thesignal indicative of the brightness of the external light. In oneembodiment, a non-transitory computer readable stores instructions thatwhen executed by a processor cause the processor to perform the method.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features and other advantages of thepresent invention will be more clearly understood from the followingdetailed description taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a schematic diagram of a transparent display apparatusaccording to an exemplary embodiment of the present invention;

FIG. 2A is a schematic cross-sectional view of the transparent displayapparatus according to an exemplary embodiment of the present invention;

FIGS. 2B and 2C are schematic diagrams illustrating light incident ontothe transparent display apparatus according to the exemplary embodimentof the present invention;

FIG. 2D is a graph for describing a control of the light control unit ofthe transparent display apparatus according to the exemplary embodimentof the present invention;

FIG. 3 shows schematic diagrams illustrating a light control unit of thetransparent display apparatus according to the exemplary embodiment ofthe present invention;

FIG. 4 is a schematic diagram of a transparent display apparatusaccording to an exemplary embodiment of the present invention;

FIG. 5 is a block diagram of a transparent display apparatus accordingto an exemplary embodiment of the present invention;

FIG. 6A is a block diagram of a light transmittance control deviceaccording to an exemplary embodiment of the present invention;

FIG. 6B is a block diagram of a light transmittance control deviceaccording to various exemplary embodiments of the present invention;

FIGS. 7A to 9B are schematic diagrams of a transparent display apparatusaccording to various exemplary embodiments of the present invention;

FIG. 10 is a graph for describing a change of shielding rate and ameasured value of the optical sensor of the present invention;

FIG. 11 is a flowchart illustrating a method for controlling atransparent display apparatus according to an exemplary embodiment ofthe present invention; and

FIG. 12 shows schematic diagrams of apparatuses to which the transparentdisplay apparatus according to the exemplary embodiment of the presentinvention is applicable.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Various advantages and features of the present invention and methodsaccomplishing thereof will become apparent from the followingdescription of embodiments with reference to the accompanying drawings.However, the present invention is not limited to exemplary embodimentdisclosed herein but will be implemented in various forms. The exemplaryembodiments are provided by way of example only so that a person ofordinary skilled in the art can fully understand the disclosures of thepresent invention and the scope of the present invention. Therefore, thepresent invention will be defined only by the scope of the appendedclaims.

Indicating that elements or layers are “on” other elements or layersinclude both a case in which the corresponding elements are just aboveand directly contacting other elements and a case in which thecorresponding elements are intervened with other layers or elements.

Although first, second, and the like are used in order to describevarious components, the components are not limited by the terms. Theabove terms are used only to distinguish one component from the othercomponent. Therefore, a first component mentioned below may be a secondcomponent within the technical spirit of the present invention.

In the drawings, size and thickness of each element are arbitrarilyillustrated for convenience of description, and the present invention isnot necessarily limited to those illustrated in the drawings.

Hereinafter, exemplary embodiments of the present invention will bedescribed with reference to the accompanying drawings.

FIG. 1 is a schematic diagram of a transparent display apparatusaccording to an exemplary embodiment of the present invention. Atransparent display apparatus 100 according to the exemplary embodimentof the present invention includes a transparent display unit 110, alight control unit 120, and an optical sensor 150.

The transparent display apparatus 100 in the present specification meansa display apparatus in which at least a partial area of a screen of thedisplay apparatus that is seen by a user is transparent. External lightis transmitted through the transparent display apparatus 100, and thetransparent display apparatus 100 self-emits light at the same time. Theuser of the transparent display apparatus 100 simultaneously receivesinformation transmitted through the external light and informationtransmitted from the display apparatus itself. That is, informativenessin the transparent display apparatus 100 is divided into informativenessof a video displayed on the transparent display apparatus 100 andinformativeness of a background on a back surface of the transparentdisplay apparatus 100 through the external light.

Further, visibility of the transparent display apparatus 100 is dividedinto visibility of the video displayed on the transparent displayapparatus 100 and visibility of the background on the back surface ofthe transparent display apparatus 100.

In terms of the visibility of the displayed video, the background on theback surface of the transparent display apparatus 100 is recognized asinterference or noise for the displayed video. That is, in terms of thevisibility of the displayed video, as the amount of light incident fromthe back surface is small, the visibility of the displayed video isimproved. However, in order to improve the visibility of the displayedvideo, when the light incident from the back surface is completelyblocked in the transparent display apparatus 100, since theinformativeness of the background on the back surface of the transparentdisplay apparatus 100 is also blocked, a major function of thetransparent display apparatus 100 is lost.

The transparent display apparatus 100 according to the exemplaryembodiment of the present invention is configured to maintaininformativenss of the background on the back surface of the transparentdisplay apparatus 100 while improving the visibility of the displayedvideo in the transparent display apparatus 100.

An ambient environment projected to the transparent display apparatus100 has various brightness environments. Brightness means the amount oflight in lux that is measured by an illuminated sensor. For example, thebrightness in an office is about 200 to 500 lux, the brightness in theshade of a building or forest in the daytime is about 20,000 to 30,000lux, and the brightness in the sun in the daytime is about 50,000 to100,000 lux. Due to such a brightness environment, there are variousvariables that are involved in the brightness of light incident onto thetransparent display apparatus 100.

The user's eye varies depending on the brightness environment. Forexample, the user′ eye is capable of clearly seeing a video with lowluminance under the low brightness environment of 200 lux, but is notcapable of clearly seeing a video with low luminance under thebrightness environment of 30,000 lux. The user′ eye is capable ofclearly seeing a video with a small amount of light or is not capable ofclearly seeing the video with high-luminance light by dilating orcontracting the pupil depending on the brightness environment.

The conventional display apparatus includes a configuration forsuppressing a surface reflection of the display apparatus so as tocorrespond to the brightness environment, but such a configuration isdesigned in consideration of only light reflected from a front surfaceof the display apparatus. In the transparent display apparatus 100according to the exemplary embodiment of the present invention, lightincident on the back surface as well as the light reflected from thefront surface is taken account of. Further, since the light incident onthe back surface of the transparent display apparatus 100 is not noisebut includes information that the user needs, the luminance of a videodisplayed by the transparent display apparatus and the light incident onthe back surface need to be balanced under the various brightnessconditions. That is, by appropriately maintaining a balance between thedisplayed video and intensity of the light incident on the back surface,it is possible to achieve optimum visibility of the displayed video andthe background video.

The transparent display apparatus 100 according to the exemplaryembodiment of the present invention measures characteristics of lightincident from a light source 140 by using the optical sensor 150 andadjusts light transmittance of the light control unit 120 on the basisof the measured characteristics of light, so that it is possible tomaximize the visibility of an object 130 displayed on the transparentdisplay unit 110 and the informativeness of the background on the backsurface of the transparent display apparatus 100.

The transparent display apparatus 100 according to the exemplaryembodiment of the present invention may include various transparentdisplay units 110.

The transparent display unit 110 of the transparent display apparatus100 according to the exemplary embodiment of the present invention maybe a transparent organic light-emitting display device. The transparentorganic light-emitting display device includes an emissive area wheredisplay light is emitted and a transmissive area where incident light istransmitted through the organic light-emitting display device. Thetransparent organic light-emitting display device in the presentspecification means a display device in which a transparent organiclight-emitting display device has a transmittance of at least 20% ormore. Since the emissive area is adjacent to the transmissive area, whenlight incident on the transmissive area is excessively bright, theintensity of light in the transmissive area is relatively weak. Thus,the user of the transparent display apparatus is capable of seeing onlylight in the transmissive area. Accordingly, an ambient contrast ratiounder an ambient light condition or gamma curve characteristics underthe ambient light condition may be variably changed depending onbrightness of the transmissive area. Accordingly, by adjusting thebrightness of the transmissive area of the transparent organiclight-emitting display device or the intensity of the light incident onthe back surface of the transparent organic light-emitting displaydevice, it is possible to control a contrast ratio.

The light control unit 120 is configured to change a path of lightincident on the light control unit 120 by transmitting, scattering,absorbing or shielding the light, or change characteristics of thelight. The light control unit 120 in the present specification may beused as a shielding unit, a light shielding unit, an active shieldingfilm, an electric shutter unit, an active shading layer, or alight-transmitting unit.

The light control unit 120 can generate an area corresponding to anobject so as to improve the visibility of the object by entirely orselectively controlling the brightness of the external light incident onthe transparent display apparatus 100 so as to correspond to thetransmissive area of the transparent display apparatus 100.

The controlling of the transmittance of the light incident on thetransparent display apparatus 100 is closely relevant to how much of theincident light is absorbed or transmitted through the transparentdisplay apparatus. When optical reflectivity of the light control unit120 is high, the light from the back surface can be blocked. However,since the light control unit has high reflectivity, the light incidentfrom the front surface is reflected, so that the visibility of thetransparent display apparatus 100 is degraded. Accordingly, the lightcontrol unit 120 of the transparent display apparatus 100 according tothe exemplary embodiment of the present invention may have a lighttransmittance of 1% to 90%, and the reflectivity of the light controlunit 120 may be 10% or less. The light transmittance of the lightcontrol unit 120 may be represented as a plurality of gradation levels.

Furthermore, the light control unit 120 of the transparent displayapparatus 100 according to the exemplary embodiment of the presentinvention may be a MEMS (Micro Electro Mechanical System) device. TheMEMS device includes a substrate, thin-film layers, an air layer, and areflection film layer. In the MEMS device, a screen is displayedaccording to two states of an open state and a collapsed state. In theMEMS device, when a voltage is not applied, the thin-film layers areseparated, so that selective reflection can be carried out. When a lowvoltage is applied to generate an electrostatic force, the reflectionfilm layer is moved to absorb light.

Moreover, the light control unit 120 of the transparent displayapparatus 100 according to the exemplary embodiment of the presentinvention may be an electro wetting device or an electro chromic device.However, for the sake of convenience in description, a case where thelight control unit 120 of the transparent display apparatus 100 is alight control unit 120 in which light transmittance is determined bycharged particles will be described below.

The front surface and the back surface of the transparent displayapparatus 100 in the present specification are defined in view of lightemitted from the transparent display apparatus 100. In the presentspecification, the front surface of the transparent display apparatus100 means a surface on which light is emitted from the transparentdisplay apparatus 100, and the back surface of the transparent displayapparatus 100 means a surface opposite to the surface on which light isemitted from the transparent display apparatus 100. The transparentdisplay apparatus 100 includes the transparent display unit 110 and thelight control unit 120, and the light control unit 120 may be disposedon the front surface or the back surface of the transparent display unit110 and overlap with the transparent display unit 110. The light controlunit 120 is preferably disposed on the back surface of the transparentdisplay unit 110 to control the light from the back surface.

Referring to FIG. 1, for sake of convenience in description, althoughthe transparent display unit 110 and the light control unit 120 aredistanced from each other, the transparent display unit 110 and thelight control unit 120 may be bonded by an adhesive or glue or may bepositioned sufficiently close to each other so as to be driven as atleast one transparent display apparatus 100.

Since the light control unit 120 and the transparent display unit 110have the same resolution, an area displayed by the transparent displayunit 110 and an area controlled by the light control unit 120 aresubstantially the same. Alternatively, the transparent display unit 110and the light control unit 120 may have different resolutions. Forexample, the resolution of the light control unit 120 may be lower thanthe resolution of the transparent display unit 110. In such a case, adriving algorithm for allowing the resolution of the transparent displayunit 110 to be compatible with the resolution of the light control unit120 may be further provided. Otherwise, the light control unit 120 maybe controlled as a whole. In other words, the entire area of the lightcontrol unit 120 may be controlled as one pixel.

The optical sensor 150 of the transparent display apparatus 100according to the exemplary embodiment of the present invention is adevice that detects the characteristics of the incident light andconverts the detected characteristics of the light into an electricsignal indicative of the detected characteristics of the light. Theoptical sensor 150 may be a photoconductive effect optical sensor or aphotovoltaic effect optical sensor. The photoconductive effect opticalsensor includes a CdS (Cadium Sulfide) photoconductive cell and a PbS(Lead sulfide) photoconductive cell, and the photovoltaic effect opticalsensor may include a photo diode, a photo transistor and a LASCR (LightActivated SCR). The optical sensor 150 may include a light emitting partand a light receiving part.

The optical sensor 150 of the transparent display apparatus 100according to the exemplary embodiment of the present invention may beclassified according to functions. That is, the optical sensor 150includes an illuminated sensor for measuring the brightness of thelight, a color temperature sensor for measuring a color temperature, adistance measurement sensor for measuring a distance, and a photointerrupter that detects an object.

Referring to FIG. 1, in the transparent display apparatus 100 accordingto the exemplary embodiment of the present invention, the optical sensor150 is disposed on one surface of the light control unit 120. An object130 is displayed on the transparent display unit 110, and a viewerpositions on the front surface of the transparent display unit 110. InFIG. 1, the light source 140 is positioned on the back surface of thelight control unit 120, and incident external light is explained usingarrows in the following description.

The light source 140 means all kinds of light sources in which light isallowed to be incident onto the transparent display apparatus 100according to the exemplary embodiment of the present invention byemitting or reflecting the light. The light source 140 may be the sun,and may include all kinds of lightings that emit light. In addition, thelight source 140 may include all objects that reflect light. The lightsource 140 is not limited, but may include all of the light sources 140of light incident onto the transparent display apparatus 100. Further,the light source 140 may emit light having any wavelength. Hereinafter,a case where light having a visible area is emitted will be explainedbelow.

The transparent display unit 110 of the transparent display apparatus100 according to the exemplary embodiment of the present inventiondisplays the object 130, and the optical sensor 150 measures thecharacteristics of the light incident from the light source 140 andadjusts the light transmittance of the light control unit 120 on thebasis of the measured characteristics of the light. By adjusting thelight transmittance of the light control unit 120, the portion of theexternal light passing through the transparent display unit 110 isadjusted. The transparent display apparatus 100 allows the light controlunit 120 to be transparent or not to be transparent in order to realizethe adjusted light transmittance. FIG. 1 illustrates the light controlunit 120 that controls the light to become the adjusted lighttransmittance. In the transparent display apparatus 100 according to theexemplary embodiment of the present invention, the characteristics ofthe light incident onto the transparent display apparatus 100 ismeasured by the sensor, and the transparent display unit 110 or thelight control unit 120 is adjusted based on the measured characteristicsof the light. Thus, the transparent display apparatus 100 havingimproved visibility while being less affected by an external environmentis realized.

The visibility in the transparent display apparatus 100 may be measuredusing, for example, a contrast ratio of a video. In addition to thecontrast ratio, a determination criterion of the visibility in thetransparent display apparatus 100 may be different depending on variousconditions such as luminance, color sensitivity, and resolution, or maybe different depending on users. Hereinafter, a case where thedetermination criterion is the contrast ratio will be described below.However, the transparent display apparatus according to the exemplaryembodiment of the present invention is not interpreted as being limitedto the contrast ratio, but the improvement of the visibility may berepresented according to different determination criteria.

The contrast ratio means a ratio of maximum luminance to minimumluminance in the transparent display apparatus. The maximum luminance istypically luminance measured when a full-white video is input. As thecontrast ratio is high, a more excellent quality can be typicallyrealized. The contrast ratio is divided into a dynamic contrast ratio, astatic contrast ratio, a darkroom contrast ratio and an ambient contrastratio. Hereinafter, it is interpreted that the contrast ratio means thestatic and ambient contrast ratios, but the dynamic and darkroomcontrast ratios may be used as the contrast ratios in the transparentdisplay apparatus according to the exemplary embodiment of the presentinvention.

The contrast ratio in the transparent display apparatus 100 is affectedby the brightness environment. The light incident on the front surfaceof the transparent display apparatus 100 decreases the contrast ratio ofthe transparent display apparatus 100 by being reflected from thetransparent display apparatus 100 and then being seen by the user, sothat contrast is decreased. The light incident on the back surface ofthe transparent display apparatus 100 decreases the contrast ratio ofthe transparent display apparatus 100 by being seen by the user throughthe transmissive area of the transparent display apparatus 100.

The light incident on the front surface of the transparent displayapparatus 100 is reflected by at least 1% to 5%, and the light incidenton the back surface of the transparent display apparatus 100 istransmitted by, for example, 20% when taking account of only the selflight transmittance of the transparent display apparatus 100. That is,the contrast ratio in the transparent display apparatus 100 depends onthe ambient brightness environment, and, specifically, depends on thelight incident on the back surface.

TABLE 1 200 lux 2000 lux Brightness White Black Contrast White BlackContrast environment (nit) (nit) ratio (nit) (nit) ratio Incident on 2033 66.66:1 230 30 7.6:1 front surface Incident on 240 40    6:1 600 4001.5:1 back surface

Table 1 shows white/black luminance and a contrast ratio of a displayapparatus in which 1.5% of light incident on a front surface isreflected under the brightness environments of 200 lux and 2000 lux andthe transparent display apparatus 100 in which 20% of light incident ona back surface is transmitted.

Referring to Table 1, the contrast ratio in the transparent displayapparatus 100 is affected by both light incident on the front surfaceand light incident on the back surface. However, when taking account ofonly the brightness environment of 200 lux, a decrease in the contrastratio caused by the light incident on the back surface is morenoticeable than that the decrease in the contrast ratio caused by thereflection of the light incident on the front surface. Accordingly, thetransparent display apparatus 100 controls the amount of the lightincident on the back surface so as to improve the contrast ratio.

Hereinafter, a specific configuration of a transparent display apparatusaccording to an exemplary embodiment of the present invention will bedescribed.

FIG. 2A is a schematic cross-sectional view of the transparent displayapparatus according to an exemplary embodiment of the present invention.FIG. 2A illustrates a transparent display unit 210 and a light controlunit 230. The transparent display unit 210 may be a transparent organiclight-emitting display device in which a video is displayed, and thelight control unit 230 may be a charged-particle control device in whichlight transmittance is controlled.

The transparent display unit 210 includes an emissive area EA and atransmissive area TA. The emissive area EA is also referred to as anemissive part, and the transmissive area TA is also referred to as atransmissive part. The emissive area EA is an area where an actual imageis realized, and the transmissive area TA is an area where at least aportion of external light from a back surface of a transparent displayapparatus 200 is transmitted. Accordingly, when the transparent organiclight-emitting display device is not driven, the user is capable ofseeing a background through the transmissive area TA, namely, an objectof a back surface of the transparent display apparatus 200. Meanwhile,when the transparent display apparatus 200 is driven, the user iscapable of simultaneously seeing a video of the emissive area EA and thebackground through the transmissive area TA. Although it has beenillustrated in FIG. 2A that an area of the transmissive area TA of asub-pixel region is greater than that of the emissive area EA, an arearatio of the emissive area EA to the transmissive area TA in thesub-pixel region may be variously set in terms of visibility andtransmittance.

Hereinafter, a specific configuration of the transparent displayapparatus 200 will be described. A configuration of the transparentdisplay unit 210 is first described, and a configuration of the lightcontrol unit 230 is described.

Referring to FIG. 2A, the transparent display unit 210 includes a firstsubstrate 211, an active layer 212, a gate insulating film 213, a gateelectrode 214, an interlayer insulating film 215, a source electrode 216b, a drain electrode 216 a, an overcoat layer 217, a reflective layer218, an anode 219, an organic light-emitting layer 220, a cathode 221,and a bank layer 222. The active layer 212, the gate insulating film213, the gate electrode 214, the interlayer insulating film 215, thesource electrode 216 b and the drain electrode 216 a constitute athin-film transistor, and the anode 219, the organic light-emittinglayer 220 and the cathode 221 constitute an organic light-emittingdiode. The organic light-emitting diode includes a sealing part 223, acolor filter 224, and a second substrate 225. FIG. 2A illustrates a casewhere the transparent display unit 210 is a top-emission type organiclight-emitting display device.

The specific configuration of the light control unit 230 is describedbelow.

Referring to FIG. 2A, the light control unit 230 includes a thirdsubstrate 231, an active layer 232, a gate insulating film 233, a gateelectrode 234, an interlayer insulating film 235, a source electrode 236b, a drain electrode 236 a, an overcoat layer 237, first electrodes 238,a second electrode 240, protection layers 241 and 242, a fluid 244including charged particles 245, and partition walls 243.

The light control unit 230 is attached to the transparent display unit210. Referring to FIG. 2A, the transparent organic light-emittingdisplay device is disposed on the light control unit 230 by using atransparent adhesive or a transparent adhesive layer. In FIG. 2A,although it has been illustrated that the light control unit 230 isdisposed under the transparent display unit 210, the light control unit230 may be formed on the transparent display unit 210. The light controlunit 230 and the transparent display unit 210 of the transparent displayapparatus 200 may be independently driven, and may selectively controlincident light.

FIG. 2B is a schematic diagram illustrating light incident onto thetransparent display apparatus according to the exemplary embodiment ofthe present invention. FIG. 2B illustrates light incident on one lightreceiving point of the back surface of the transparent display apparatus200. Although not specifically mentioned, the “light incident orincident light” in the present specification means light incident on onesurface of the transparent display apparatus 200. The light incident onthe one surface of the transparent display apparatus 200 can be measuredby the illuminated sensor included in the area of the transparentdisplay apparatus 200 where light is not emitted or any sensor disposedto measure the incident light.

Referring to FIG. 2B, the light incident on the one surface of thetransparent display apparatus 200 may include all kinds of lightincident at an angle of 0° to 180° with respect to the substrate as wellas light vertically incident onto the transparent display apparatus 200.However, for the sake of convenience in description, although incidentlight which has quadrature components by being incident onto thetransparent display apparatus 200 at a right angle or by being refractedin the transparent display apparatus 200 is described, incident lightnot having the quadrature components may be described similarly to theincident light that enters at a right angle.

FIG. 2C illustrates the light incident onto the transparent displayapparatus 200 according to the exemplary embodiment of the presentinvention according to the light controlling of light control units 230a, 230 b, and 230 c. Furthermore, the transparent display apparatus 200include the light control units 230 a, 230 b and 230 c, and the lightcontrol units 230 a, 230 b and 230 c have different light transmittancevalues depending on the applying duration of a voltage or intensity ofthe voltage.

The transparent display apparatus 200 selectively shields incident lightof the transparent display apparatus 200 by controlling the lightcontrol units 230 a, 230 b and 230 c to adjust the contrast ratio of thetransparent display apparatus 200.

The contrast ratio may be defined a value obtained by dividing maximumluminance of a video by minimum luminance. The contrast ratio of thetransparent display apparatus 200 in the present specification iscalculated so as to include luminance of light, which has entered theback surface of the transparent display apparatus 200 and has beentransmitted except for surface-reflection luminance of the transparentdisplay unit from the external light. Accordingly, the contrast ratio inthe transparent display apparatus 200 is a value obtained by dividing(maximum luminance of video+luminance of transmitted back-surface light)by (minimum luminance of video+luminance of transmitted back-surfacelight).

${{contrast}\mspace{14mu} {ratio}} = {{X\text{:}1} = {\frac{L_{\max} + {L_{back} \times T_{self} \times T_{var}}}{L_{\min} + {L_{back} \times T_{self} \times T_{var}}}\text{:}1}}$

wherein Lmax is maximum luminance, Lmin is minimum luminance, Lback isbrightness of back-surface light of the transparent display apparatus,Tself is self light transmittance of the transparent display apparatusand is generally a fixed value attributed to the elements on thetransparent display apparatus that may block light (OLED, metal lines,imperfections in materials, etc), and Tvar is the light transmittance oflight control units 230 a, 230 b and 230 c of the transparent displayapparatus.

The maximum luminance means the highest luminance capable of beingrepresented by the transparent display apparatus, and is assumed as, forexample, 400 nit. The minimum luminance is the lowest luminance capableof being represented by the transparent display apparatus 200 and isassumed as 0.01 nit, for example.

The “transmitted back-surface light” means light, which has entered theback surface of the transparent display apparatus 200 and has passedthrough the transparent display apparatus 200, and the luminance of thetransmitted back-surface light is luminance to which the self lighttransmittance of the transparent display apparatus 200 is applied. Thatis, the luminance of the transmitted back-surface light is luminance towhich the Tself and the Tvar are applied to the Lback in combination.

It is assumed that the brightness of the light incident on the backsurface is 200 lux and the self light transmittance is 0.4 (40%), butthe self light transmittance may vary depending on the configuration ofthe transparent display apparatus 200.

Since the transparent display apparatus 200 including the light controlunits 230 a, 230 b and 230 c can control the luminance of the lightincident on the back surface that passes through the transparent displayunit 210, the transmittance of the light control unit acts on theluminance of the incident light on the back surface as variables. Here,the light transmittance is light transmittance controlled by the lightcontrol units 230 a, 230 b and 230 c of the transparent displayapparatus 200 and is represented as a normalized value of 0 to 1.

In (a), (b), and (c) of FIG. 2C, it is assumed that light rays havingthe same intensities are emitted in the emissive part and light raysincident onto the transparent display apparatus 200 are constant. In (a)of FIG. 2C, the light control unit 230 a is controlled to allow all theincident light rays to be transmitted. When the light control unit 230 ais controlled to allow all the incident light rays to be transmitted,the user sees both light emitted from the emissive part and lightincident from the back surface of the transparent display apparatus 200.

At this time, when assuming that the transmittance of the light controlunit 230 a is 100%, a contrast ratio can be calculated by using theaforementioned contrast-ratio equation. The transmittance of 100% is anideal value, and the transmittance of 100% in the present inventionmeans substantial maximum transmittance capable of being realized by thelight control unit. In one embodiment, an ambient contrast ratio of thetransparent display apparatus is at least 6:1 when the brightness of theexternal light measured by said one or more optical sensors is 500 luxor less.

${(a)\mspace{14mu} {contrast}\mspace{14mu} {ratio}} = {{6\text{:}1} = {\frac{400 + {200 \times 0.4 \times 1.0}}{0.01 + {200 \times 0.4 \times 1.0}}\text{:}1}}$

In (b) of FIG. 2C, the light control unit 230 b is controlled to allow apart of incident light to be transmitted. When the light control unit230 b is controlled to allow a part of incident light to be transmitted,since the user is capable of more clearly seeing emitted light ascompared to (a) of FIG. 2C, the visibility of the transparent displayapparatus is relatively improved.

It is assumed that the transmittance of the light control unit 230 b is50% with reference to values in (a) of FIG. 2C, and the contrast ratiois calculated.

${(b)\mspace{14mu} {contrast}\mspace{14mu} {ratio}} = {{11\text{:}1} = {\frac{400 + {200 \times 0.4 \times 0.5}}{0.01 + {200 \times 0.4 \times 1.0}}\text{:}1}}$

In (c) of FIG. 2C, the light control unit 230 c is controlled to furtherdecrease the transmittance of the incident light. When the light controlunit 230 c is controlled to further shield the incident light, since theuser is capable of more clearly seeing emitted light as compared to (a)and (b) of FIG. 2C, the visibility of the transparent display apparatusis improved, but it may be difficult to see the object on the backsurface of the transparent display apparatus 200.

It is assumed that the transmittance of the light control unit 230 c is10% with reference to values in (a) of FIG. 2C, and the contrast ratiois calculated.

${(c)\mspace{14mu} {contrast}\mspace{14mu} {ratio}} = {{51\text{:}1} = {\frac{400 + {200 \times 0.4 \times 0.1}}{0.01 + {200 \times 0.4 \times 0.1}}\text{:}1}}$

Referring to (a), (b) and (c) of FIG. 2C and the contrast ratios, it canbe seen that the contrast ratios in the transparent display apparatus200 depends on the maximum luminance of the transparent displayapparatus 200, the self transmittance of the transparent displayapparatus 200, and the transmittance of the light control units 230 a,230 b and 230 c, and the minimum luminance does not affect a variationin the contrast ratio due to a luminance difference with the incidentlight.

The transparent display apparatus 200 according to the exemplaryembodiment of the present invention achieves a required contrast ratioby using the aforementioned contrast-ratio equations. The transparentdisplay apparatus 200 is configured to achieve a target contrast ratiothat is set by the user or is determined by the transparent displayapparatus 200.

The target contrast ratio may be a minimum contrast ratio that isrequired to see the video in the transparent display apparatus 200.Alternatively, the target contrast ratio may be a contrast ratio forallowing informativeness of the background on the back surface andinformativeness of the video to be optimally balanced.

After the transparent display apparatus 200 is set the target contrastratio, the transparent display apparatus 200 achieves the targetcontrast ratio by adjusting controllable variables in the aforementionedequations. The Lmin, Lmax, and Tself are generally considered asprospective characteristics of a display. The incident light is resultedfrom the self light transmittance of the transparent display unit 210,and the Tself is resulted from characteristics of the transparentdisplay unit 210. The transparent display apparatus 200 continuouslymeasures Lback, which is the amount of light incident on the backsurface through the optical sensor such as the illuminated sensor. Atthe same time, as stated above, the transparent display apparatus 200achieves the target contrast ratio by controlling the Tvar, which is thetransmittance of the light control units 230 a, 230 b, and 230 c. Forexample, when the target contrast ratio of the transparent displayapparatus 200 is 6:1, the transparent display apparatus 200 continuouslyupdates the Lback from the optical sensor and continuously adjusts theTvar on the basis of the updated Lback, so that the contrast ratio ofthe transparent display apparatus 200 is maintained to be approximate tothe target contrast ratio.

In addition, in various exemplary embodiments, by adjusting a gammavoltage of the transparent display apparatus 200, it is possible toadjust the Lmax as the maximum luminance. The maximum luminance isdetermined by a gamma voltage generating unit included in the displayapparatus. The gamma voltage generating unit converts a digital inputvideo into an analog voltage and applies the converted voltage to theorganic light-emitting layer 220 of the emissive area EA. The gammavoltage generating unit generates a gamma voltage corresponding to theinput video by using a plurality of registers. The maximum luminance canbe adjusted by controlling a maximum value of the gamma voltagecorresponding to the input video. The transparent display apparatus 200increases the gamma voltage to increase or decrease the luminance of thetransparent display unit 210, so that the transparent display apparatuscan achieve the target contrast ratio.

In the transparent display apparatus 200 according to the exemplaryembodiment of the present invention, by controlling the transmittance ofthe light control units 230 a, 230 b and 230 c, it is possible togreatly improve the contrast ratio, and it is possible to control thetransparent display apparatus 200 so as to enhance the visibility fromthe point of view of the user of the transparent display apparatus 200.

FIG. 2D is a graph for describing a control of the light control unit ofthe transparent display apparatus according to the exemplary embodimentof the present invention. An X-axis in the graph represents brightness(Lux) of light incident on the back surface, and shielding raterepresents a degree of shading light by the light control unit. Theshielding rate is in inverse proportion to the transmittance. That is,as the transmittance is increased, the shielding rate is decreased, andas the shielding rate is increased, the transmittance is decreased. Whenthe target contrast ratio is set to 2:1, line X in the graph representsthe shielding rate of the light control unit required depending on thebrightness. The shielding rate is calculated using the followingequation.

$T_{var} = {\frac{\left( {\frac{L_{\max}}{CR} - L_{\min}} \right)}{L_{back} \times {T_{self}\left( {1 - \frac{1}{CR}} \right)}} \approx \frac{\left( \frac{L_{\max}}{CR} \right)}{L_{back} \times {T_{self}\left( {1 - \frac{1}{CR}} \right)}}}$

Here, the transmittance Tvar of the light control unit is obtained bysubtracting the shielding rate from 1. Lmax, Lmin, Lback and Tself arethe same values as those in FIG. 2C. CR represents a target contrastratio. The equation of Tvar is obtained by arranging the contrast-ratioequation in FIG. 2C for the Tvar. Since the Lmin is a small value, theLmin may be omitted for the sake of convenience in calculation. (a) ofFIG. 2D is a graph that represents a relation between the Lback and theTvar when the CR is set to 2, the Tself is set to 0.2, and the Lmax isset to 400.

Reference brightness values for determining a zone A, a zone B and azone C is derived from the preceding equation. For example, thereference brightness values of the zone A and the zone B correspond tobrightness values when the shielding rate is changed from 0 to a valueof 0 or more, and the reference brightness values of the zone B and thezone C correspond to brightness values when the shielding rate ischanged to a value of 0.9 or more.

Line X means shielding rate according to the Tvar equation. Hereinafter,the description is focused on line X. The reference brightness values ofthe zone A and the zone B are 1200 lux, and in the zone A where thebrightness is in a range of 0 to 1200 lux, even when the shielding rateof the light control unit is 0, it is possible to maintain CR of 2 ormore. That is, in zone A, even though the light control unit is operatedin a transparent state, since the required contrast ratio is achieved,the light control unit is operated in the transparent state to maximizethe amount of light passing through the display apparatus. In oneembodiment, the reference brightness value between zone A and zone B isbetween 300 to 1500 lux.

Meanwhile, the reference illumination values of the zone B and the zoneC are 8400 lux, and in the zone B where the brightness is in a range of1200 Lux to 8400 Lux, the shielding rate of the light control unit isvaried depending on the brightness, so that it is possible to maintainCR of 2 or more. When the brightness of the light incident on the backsurface corresponds to the zone B, the light control unit is operated ina translucent state. In one embodiment, the reference brightness valuebetween zone B and zone C is between 6000 to 15000 lux.

In the zone C where the brightness is 8400 Lux or more, the shieldingrate of the light control unit is 0.9 or more. When the shielding rateis 0.9 or 90% or more, it is determined that an effect of thetranslucent state is marginal, and the light control unit issubstantially in a shield state. Thus, in the zone C, the light controlunit is preferably operated in the shield state. That is, when theshielding rate is 90% or more, the informativeness of the back surfaceof the light control unit is degraded, and the contrast ratio is alsodecreased. In order to minimize such a phenomenon, when the shieldingrate is 90% or more, the light control unit is realized to be operatedin a state in which the shielding rate is 100% to minimize the amount oflight passing through the display apparatus. The shield state of 90% ormore is a value exhibiting a substantial shield effect verified throughan experiment result, and the shield state may be naturally set to ahigher value.

When the light control unit is operated in the translucent state in thezone B, the shielding rate of the light control unit can be continuouslyvaried as shown in line X. The light control unit can vary the shieldingrate by adjusting magnitude or width of a voltage applied depending onthe shielding rate.

Line Y is a look-up table value that is set by a result throughrepetition experiments. The shielding rate of the light control unit canbe varied in plurality of steps depending on the brightness of the lightmeasured by the optical sensor such that the light control unit has aconstant shielding rate for a constant zone such as line Y. Althoughline Y simplifies the shielding rate depending on the brightness ascompared to that in line X, the realization is simple and similar shieldeffect can be exhibited.

Meanwhile, as the set target contrast ratio is varied, a range ofbrightness values to which the transparent state, the translucent state,and the shield state are applied is varied. For example, when the targetcontrast ratio is increased, the maximum brightness to which thetransparent state is applied is decreased, and the minimum brightness towhich the shield state is applied is also decreased. Accordingly, inorder to realize one or more target contrast ratios, the look-up tableis preferably implemented as a look-up table that stores information ona plurality of target contrast ratios.

(b) of FIG. 2D is a graph showing a relation between Lback and Tvar whenthe target contrast ratio is 7:1. When compared to (a) of FIG. 2D, (b)of FIG. 2D illustrates that brightness at the shielding rate of 0 andbrightness at the shielding rate of approximately 1.0 are relativelylower than those in the target contrast ratio of 2:1. Eventually, astate reference of the light control unit as well as the shielding rateof the light control unit is varied depending on the target contrastratio.

FIG. 3 shows schematic diagrams illustrating a light control unit of thetransparent display apparatus according to the exemplary embodiment ofthe present invention. In (a) and (b) of FIG. 3, a third substrate 310,a fourth substrate 320, a first electrode 330, a second electrode 340,partition walls 360, a protection layer 350 and a fluid 380 are the sameas the third substrate 231, the fourth substrate 239, the firstelectrode 238, the second electrode 240, the partition walls 243, theprotection layers 241 and 242 and the fluid 244 described in FIG. 2A.Thus, the redundant descriptions thereof are not presented.

In (a) of FIG. 3, light incident onto a light control unit 300 passesthrough the third substrate 310, reaches black charged particles 370,and is then absorbed by the black charged particles 370. Since theincident light is shielded by an arrangement of the black chargedparticles 370, such a state of the transparent display apparatus iscalled a shield state.

In (b) of FIG. 3, light incident on the light control unit 300sequentially passes through the third substrate 310, the secondelectrode 340, and the fourth substrate 320. The black charged particles375 are arranged in a manner that does not block the light. Such a stateof the light control unit 300 is called a transmissive state or atransparent state.

Alternatively, only a part of the incident light is transmitted betweenthe black charged particles. Since the transmitted part of the light istransmitted through the transmissive area, the object on the backsurface of the transparent display apparatus can be seen at an upperpart of the transparent display apparatus. The remaining part of theincident light reaches the black charged particles and is absorbed bythe black charged particles. Since the incident light is transmitted orshielded by the spread of the black charged particles 370 and 375, sucha state of the light control unit 300 is called a translucent state.

In the translucent state in which only a part of the incident light istransmitted, the transmittance is variably controlled depending on anapplying time or applying magnitude of a voltage applied to the firstelectrode 330 or the second electrode 340 of the light control unit 300.

FIG. 4 is a schematic diagram of a transparent display apparatusaccording to an exemplary embodiment of the present invention. Atransparent display apparatus 400 includes a processing unit 410, atransparent-display-unit timing controller 421, atransparent-display-unit panel 420, a transparent-display-unit datadriving unit 422, a transparent-display-unit scan driving unit 423, alight-control-unit timing controller 431, a light-control-unit panel430, a light-control-unit data driving unit 432, and alight-control-unit scan driving unit 433.

The timing controllers 421 and 431 may be formed on one integratedcircuit or may be patterned on the panels, and the timing controllers421 and 431 and the data driving units 422 and 432 may be provided invarious forms such as COG (Chip on Glass), COF (Chip on Film), PCB, andFPCB (Flexible Circuit Board).

The processing unit 410 provides video data to thetransparent-display-unit timing controller 421 and light control data tothe light-control-unit timing controller 431. The light control data maybe data for selectively shielding incident light, and may be providedtogether with a data signal to the light-control-unit timing controller431 or may be separately provided to the light-control-unit timingcontroller.

The processing unit 410 may generate a synchronization signal andprovide the generated synchronization signal to thetransparent-display-unit timing controller 421 and thelight-control-unit timing controller 431 so as to allow the transparentdisplay unit and the light control unit to be time-synchronized. Thesynchronization signal may be generated to be synchronized to a panelhaving a slow response speed of the transparent display unit and thelight control unit.

The transparent display unit includes the transparent-display-unittiming controller 421, the transparent-display-unit panel 420, thetransparent-display-unit data driving unit 422, thetransparent-display-unit scan driving unit 423, and a power supply unit424.

The transparent-display-unit timing controller 421 may be referred to asa transparent-display-unit driving unit, and thetransparent-display-unit driving unit generates a scan control signal onthe basis of the video to control the transparent-display-unit scandriving unit 423, and generates a data signal to control thetransparent-display-unit data driving unit 422.

The transparent-display-unit data driving unit 422 receives the datasignal from the transparent-display-unit timing controller 421. Thetransparent-display-unit data driving unit 422 converts the data signalinto the corresponding gamma voltage, and determines the amount ofcurrent flowing in the anode and the cathode of the organiclight-emitting diode to control a degree of emitting of thecorresponding pixel. When the gamma voltage is adjusted, since themaximum luminance of the transparent display apparatus 400 is varied,the contrast ratio of the transparent display apparatus 400 is varied.The transparent display apparatus 400 can adjust the gamma voltage toachieve a target contrast ratio, and can continuously the gamma voltageto maintain the target contrast ratio.

The transparent-display-unit scan driving unit 423 is operated such thatscan lines are driven and the data signal is input to sub-pixelscorresponding to the scan lines. The transparent-display-unit scandriving unit 423 may provide one scan line signal or a plurality of scanline signals for selecting the scan line or a plurality of scan lines tothe transparent-display-unit panel 420.

The power supply unit 424 supplies various voltages required in thetransparent-display-unit data driving unit 422, thetransparent-display-unit scan driving unit 423 and the anode and thecathode of the transparent-display-unit panel 420. The power supply unit424 supplies ELVDD, ELVSS, VDD, and VSS. The transparent-display-unitpanel 420 includes a plurality of scan lines, a plurality of data lines,and a plurality of transparent-display-unit sub-pixels.

In order to emit the organic light-emitting layer by video informationof the input data signal, a switching thin-film transistor T1 and adriving thin-film transistor T2 are used.

Driving of the light control unit in the transparent display apparatus400 according to the exemplary embodiment of the present invention isdescribed. The light control unit may be configured and be driven in apassive matrix. The light control unit may be turned on/off as a wholeor may be controlled for each line. Alternatively, the light controlunit may be driven in an active matrix. The light-control-unit timingcontroller 431 receives the light control data from the processing unit410 as mentioned above. The light control data is data for controllingthe light transmittance so as to achieve the target contrast ratio ofthe transparent display apparatus 400. The light control data isdetermined by the light-control-unit timing controller 431 or theprocessing unit 410 of the transparent display apparatus 400.

The light-control-unit scan driving unit 433 is operated such that thescan lines are driven and the data signal is input to the pixelscorresponding to the scan lines. The light-control-unit data drivingunit 432 converts the data signal into the corresponding voltage, andsupplies the voltage and pulse to the light control unit to control thespread of the black charged particles. In other words, the transparentdisplay apparatus 400 adjusts the voltage or pulse applied to the lightcontrol unit by using the light control data, so that the lighttransmittance of the light control unit can be adjusted. As a result, itis possible to achieve the target contrast ratio.

The power supply unit supplies the voltages required in thelight-control-unit data driving unit 432 and the light-control-unit scandriving unit 433.

When the scan control signal is applied from a scan wiring, a switchingthin-film transistor T3 transmits the light control data signal from thedata line to the electrode of the light control unit to control thevoltage applied to the electrode, and the movement of the black chargedparticles distributed in the fluid is controlled by the applied voltage.

FIG. 5 is a block diagram of a transparent display apparatus accordingto an exemplary embodiment of the present invention. A transparentdisplay apparatus 500 includes a processing unit 510, a control unit515, a transparent display unit, and a light control unit. Thetransparent display unit includes a transparent-display-unit panel 540and a transparent-display-unit panel driving unit 520, and the lightcontrol unit includes a light-control-unit panel 550 and alight-control-unit panel driving unit 530. The transparent-display-unitpanel 540 and the light-control-unit panel 550 include a plurality ofpixels and sub-pixels.

The control unit 515 controls an operation of a system of thetransparent display apparatus 500. The control unit 515 may operate thesystem in response to a command of the user, and operates the systemaccording to a preset operation. The control unit 515 controls, forexample, the processing unit 510 to decrease the light transmittance onthe basis of the light characteristics from the optical sensor so as toimprove the visibility of the video displayed on the transparent displayapparatus 500 and to operate various modes of the transparent displayapparatus 500.

The control unit 515 of the transparent display apparatus 500 includesthe system. The system includes an OS (Operating System). The OS furtherincludes various modes for providing effects of the present invention tothe user. The modes are selected by the user when necessary, and,especially, a third mode is actively adapted to the ambient environmentto be selected as an optimum mode.

A first mode sets the light control unit to a transmissive state. Thefirst mode maximizes a transparent effect and thereby maximizes thelight being transmitted. However, a problem about the visibility of anexternal environment is not solved.

A second mode set the light control unit to a shield state. The secondmode maximizes a shield effect and thereby minimizes the light beingtransmitted. The visibility is enhanced as much as possible in thesecond mode. However, there is a problem that since the transmissivearea of the entire screen is shielded, a transparent display effect isnot exhibited.

The third mode is a mode for adjusting the light transmittance of thetransparent display apparatus 500 on the basis of the lightcharacteristics from the optical sensor. The transparent displayapparatus 500 in the third mode minimizes a decrease in visibility witha change in an external brightness environment and the externalenvironment. In the third mode, the visibility of the input video ismaintained while maintaining the transparent effect.

A fourth mode is a light control mode, and the fourth mode displays thevideo by the resolution of the light control unit. By blocking the powersupply of the organic light-emitting device, the organic light-emittingdevice is driven at low power. The fourth mode is specialized under theoutdoor environment and is effective when the external light isconsiderably bright. In the fourth mode, the video is realized by theshielding. The fourth mode may be selected by the user in theenvironment of very high brightness or may be operated by setting afourth mode entering reference brightness.

The operations of the control unit 515 are selected through an inputunit 560 on the system. For example, the transparent display apparatus500 includes the input unit 560, and the plurality of modes may besequentially changed whenever input signals are input through the inputunit 560. Such a physical input unit 560 can be effectively used whenthe visibility of the transparent display apparatus 500 is rapidlydecreased. When the visibility is rapidly decreased, since it isdifficult for the user to see menus displayed on the transparent displayunit, it may be difficult to select a necessary mode.

FIG. 6A is a block diagram of a light transmittance control deviceaccording to an exemplary embodiment of the present invention. A lighttransmittance control device 600 according to the exemplary embodimentof the present invention includes an optical sensor 610 and a processingunit 630 including a light transmittance determining unit 632.

The light transmittance control device 600 means a device that isconnected to the light control unit and/or the transparent display unitin the transparent display apparatus, receives the light characteristicsfrom the optical sensor 610, analyzes the received lightcharacteristics, and determines the light transmittance of the lightcontrol unit on the basis of the analysis of the light characteristics.The light transmittance control device 600 according to the exemplaryembodiment of the present invention senses the amount of light throughthe optical sensor 610, calculates the contrast ratio on the basis ofthe sensed amount of light through the processing unit 630, compares thecalculated contrast ratio with a target contrast ratio, and determinesthe transmittance of the light control unit through the lighttransmittance determining unit 632 so as to achieve the target contrastratio.

The optical sensor 610 measures characteristics of the light incident onone surface of the transparent display apparatus. The optical sensor 610measures the amount of light, the luminance of the light, a distributionof the light, and whether or not the object approaches. The opticalsensor 610 outputs the measured characteristics of the light as ananalog value, and the output value is converted into a digital value byan ADC (analog to digital) converter. The converted value is input tothe processing unit 630 including the light transmittance determiningunit 632. For example, the light transmittance control device 600calculates predetermined transmittance for the amount of light bysubstituting the sensed amount of light from the optical sensor 610 fora lookup table that is previously stored.

The light transmittance determining unit 632 determines the lighttransmittance of the light control unit on the basis of the measuredcharacteristics of the light. As described above, the lighttransmittance is controlled by the light control unit of the transparentdisplay apparatus through the light control data signal. That is, thelight control data signal is generated based on the determinedtransmittance. The light control data signal is calculated bysubstituting the light transmittance for the look-up table that ispreviously stored.

The light transmittance of the transparent display apparatus isdetermined in consideration of the target contrast ratio, especially. Byachieving the target contrast ratio, a transparency of the transparentdisplay apparatus can be maintained while ensuring the visibility of thevideo. Further, as described above, the light transmittance of thetransparent display apparatus according to the exemplary embodiment ofthe present invention can be determined in consideration of variouscharacteristics including luminance, color temperature, and chroma inaddition to the target contrast ratio.

FIG. 6B is a block diagram of a light transmittance control deviceaccording to various exemplary embodiments of the present invention.Referring to FIG. 6B, a light transmittance control device 600 includesan optical sensor 610 and a processing unit 630 including a lighttransmittance determining unit 632. The optical sensor 610 may be afront-illuminated sensor 611, a back-illuminated sensor 612, a pluralityof illuminated sensors 614, and a proximity sensor 615. Further, animage sensor 613 may be used instead of the illuminated sensor. In FIG.6B, although it has been illustrated that the optical sensor 610includes a plurality of different sensors, the optical sensor 610 may bean independent sensor among the aforementioned sensors. The opticalsensor may be at least one sensor among the front-illuminated sensor611, the back-illuminated sensor 612, the plurality of illuminatedsensors 614 and the proximity sensor 615.

The optical sensor 610 may be the front-illuminated sensor 611 disposedon the front surface of the transparent display apparatus. Thefront-illuminated sensor 611 measures brightness of light incident onthe front surface of the transparent display apparatus. When reflectedlight is generated from an interface of the transparent displayapparatus, similarly to a case where light enters from the back surfaceof the transparent display apparatus, the contrast ratio is decreased.Specifically, incident light by the sunlight or the illumination maydecrease the luminance of the displayed video, or may decrease thevisibility of the displayed video by being reflected from the interfaceof the transparent display apparatus. Further, the contrast ratio may bedecreased. The light, which has entered the front surface of thetransparent display apparatus and has been reflected may not becontrolled, and the light incident on the back surface of thetransparent display apparatus may be controlled by the light controlunit. When the luminance of the light incident on the front surface ishigh and thus likely to cause a decrease in the visibility by thereflected light, the transparent display apparatus is configured toincrease the maximum luminance of the displayed video. Further, when theluminance of the incident light is low to achieve favorable visibility,the transparent display apparatus may be configured to decrease themaximum luminance of the video to save a driving power.

The optical sensor 610 may be the back-illuminated sensor 612 positionedon the back surface of the transparent display apparatus. Theback-illuminated sensor 612 positioned on the back surface of thetransparent display apparatus measures the brightness of the lightincident on the back surface of the transparent display apparatus. Thebrightness of the light may be measure in lux as described above.

Hereinafter, an example operation of the light transmittance controldevice 600 according to the exemplary embodiment of the presentinvention will be described. If the measured amount of light incident onthe back surface is 0 lux, the transmittance of the light control unitis set to 100%. At this time, when the brightness sensed on the backsurface of the transparent display apparatus by the back-illuminatedsensor 612 of the transparent display apparatus is 200 lux, thetransmittance is varied.

In the transparent display apparatus according the exemplary embodimentof the present invention, when a target contrast ratio is set to, forexample, 10:1, the light transmittance determining unit 632 of thetransparent display apparatus determines the transmittance of the lightcontrol unit on the basis of the measured luminance of the light suchthat the transparent display apparatus has a target contrast ratio of10:1.

$\begin{matrix}{{{target}\mspace{14mu} {contrast}\mspace{14mu} {ratio}} = {{10\text{:}1} = {\frac{400 + {200 \times {.4} \times A}}{0.1 + {200 \times 0.4 \times A}}\text{:}1}}} & \left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack\end{matrix}$

Transmittance A determined by Equation 1 may be about 55%.

Further, except for a case where the brightness of the light measured bythe back-illuminated sensor 612 is changed to 400 lux, when otherconditions are the same, the transmittance A of the light control unitthat is determined to realize a target contrast ratio of 10:1 is about28%. In this case, the total transmittance of the entire transparentdisplay apparatus is 11% in consideration of the self transmittance ofthe transparent display apparatus and the variable transmittance of thelight control unit.

When the brightness of the light incident on the back surface measuredby the back-illuminated sensor 612 is increased, the light transmittancecontrol device 600 maintains the set contrast ratio by decreasing thetransmittance of the light control unit and thereby decreasing theportion of the external light incident on the back surface that passesthrough the transparent display unit. On the contrary to theaforementioned example, when the brightness of the light incident on theback surface is decreased, the light transmittance control device 600 isdynamically controlled to maintain the target contrast ratio byincreasing the transmittance of the light control unit. As the targetcontrast ratio is maintained, the light transmittance control device 600is driven as the transparent display apparatus having suitabletransmittance while maintaining sufficient visibility.

Further, the transmittance of the light may be determined by takingaccount of average luminance of the video. The contrast ratio of thedisplayed video is not taken account of. The light transmittance controlapparatus 600 according to the exemplary embodiment of the presentinvention can determine the light transmittance of the light controlunit by taking account of the maximum luminance, and the minimumluminance or the average luminance of the displayed video.

The optical sensor 610 may be the plurality of illuminated sensors 614positioned on one surface of the transparent display apparatus. Theplurality of illuminated sensors 614 measures the brightness of thelight incident at different positions on one surface of the transparentdisplay apparatus. For example, the plurality of illuminated sensors 614may be respectively arranged at corners of the transparent displayapparatus having a rectangular shape. Alternatively, the plurality ofilluminated sensors 614 is not limited to the aforementioned example,but may be formed in various areas of the transparent display apparatus.For example, the plurality of illuminated sensors 614 may beappropriately arranged at certain distances. Furthermore, the pluralityof illuminated sensors 614 may be arranged at optimized positions tocorrespond to the arrangement of the elements of the transparent displayapparatus. For example, when non-transparent elements are arranged in acertain area, the plurality of illuminated sensors 614 may be arrangedat the area where the non-transparent elements are arranged. Theplurality of illuminated sensors 614 can measure brightness values ofdifferent incident light rays. That is, the plurality of illuminatedsensors can measure brightness values of the incident light rays at therespective positions where the respective illuminated sensors arearranged. The brightness values of the light rays at the plurality ofpositions measured by the plurality of illuminated sensors 614 is inputto the light transmittance determining unit 632.

The light transmittance determining unit 632 can determine the lighttransmittance values in the areas where the plurality of illuminatedsensors 614 are positioned on the basis of the brightness values of thelight rays measured by the plurality of illuminated sensors 614 and thepositions of the plurality of illuminated sensors 614. The transparentdisplay apparatus may be applied to a large-sized transparent displayapparatus, for example, a large-sized transparent display apparatusdisposed on the outside. In the transparent display apparatus disposedon the outside, since incident positions of sunlight are changed alongwith the movement of the sun, the transparent display apparatus may beshaded by buildings and trees. Accordingly, as the position of theincident light is changed, the visibility of the transparent displayapparatus may be considerably affected. The light transmittancedetermining unit 632 of the transparent display apparatus according tothe exemplary embodiment of the present invention can adjust the lighttransmittance at the positions on the basis of the measured brightnessof the external light at the plurality of positions so as to enhanceuniformity of the luminance or contrast ratio of the displayed video.

The optical sensor 610 may be the plurality of illuminated sensors 614positioned on the front surface and the back surface of the transparentdisplay apparatus. The illuminated sensor positioned on the frontsurface measures the brightness of the light incident on the frontsurface of the transparent display apparatus, and the illuminated sensorpositioned on the front surface measures the brightness of the lightincident on the back surface of the transparent display apparatus.

In order to achieve the target contrast ratio, the light transmittancedetermining unit 632 determines the light transmittance of the lightcontrol unit by using values from the plurality of illuminated sensors614 positioned on the front surface and the back surface of thetransparent display apparatus and the following equation.

${{target}\mspace{14mu} {contrast}\mspace{14mu} {ratio}} = {{X\text{:}1} = {\frac{L_{\max} + {L_{front} \times T_{reflect}} + {L_{back} \times T_{self} \times T_{var}}}{L_{\min} + {L_{front} \times T_{reflect}} + {L_{back} \times T_{self} \times T_{var}}}\text{:}1}}$

wherein Lmax is maximum luminance, Lmin is minimum luminance, Lfront isluminance of light incident on front surface of transparent displayapparatus, Lback is luminance of light incident on back surface oftransparent display apparatus, Treflect is light reflectivity oftransparent display apparatus, Tself is self transmittance oftransparent display apparatus, and Tvar is light transmittance of lightcontrol unit. The illuminated sensor and the illuminated sensor that arerespectively positioned on the front surface and the back surface sensethe Lfront and the Lback to supply the sensed Lfront and Lback to thelight transmittance determining unit 632.

When the plurality of illuminated sensors 614 are the illuminatedsensors that are positioned on the front surface and the back surface,the light transmittance determining unit 632 achieves the set targetcontrast ratio by further taking account of light incident on the frontsurface. The light transmittance determining unit 632 receives thevalues of the Lfront and the Lback from the plurality of illuminatedsensors 614 and determines the Tvar so as to achieve the target contrastratio by using the aforementioned equation. Moreover, the lighttransmittance determining unit 632 can be controlled to adjust the valueof the Lmax to achieve the target contrast ratio. That is, in additionto adjusting the light transmittance of the light control unit, byadjusting the maximum luminance of the transparent display unit, thetarget contrast ratio can be achieved. The light transmittancedetermining unit 632 continuously receives the values of the Lfront andLback so as to maintain the target contrast ratio and adjusts the Tvarand the Lmax so as to correspond to the changed values when the valuesare changed.

FIG. 7B is a conceptual diagram for describing a position of the opticalsensor in the transparent display apparatus according to the exemplaryembodiment of the present invention and driving of the transparentdisplay apparatus according to the position of the optical sensor.Referring to FIG. 7B, a transparent display apparatus 720 includes afront-illuminated sensor 722 disposed on a front surface of thetransparent display apparatus 720 and a back-illuminated sensor 723disposed on a back surface. A thick arrow in the transparent displayapparatus 720 indicates that the transparent display apparatus 720displays the video in a direction of the viewer. The front-illuminatedsensor 722 is disposed in a non-display area of the transparent displayunit. A front light source 724 emits light toward the front surface ofthe transparent display apparatus 720. The light incident on the frontsurface of the transparent display apparatus 720 may be called directlight. A part of the direct light passes through the transparent displayapparatus 720 and the remaining part of the direct light is reflectedfrom an interface of the transparent display apparatus 720 in afront-surface direction as shown in FIG. 7B.

A light source 725 on a back surface emits light toward a back surfaceof the transparent display apparatus 720. The light incident on the backsurface of the transparent display apparatus 720 may be calledbacklight. A part of the backlight may be reflected from the interfaceof the transparent display apparatus 720 in a back-surface direction,but the backlight passes through the transparent display apparatus 720in a level of transmittance.

Referring to FIG. 7B, the direct light and the backlight are reflectedfrom or passes through the transparent display apparatus 720, and thedirect light and the backlight are seen together with the videodisplayed on the transparent display unit by the user. In the backlight,in order to compensate for a variation or a decrease in the contrastratio while maintaining informativeness of the object on the backsurface, the transparent display apparatus 720 controls thetransmittance of the light incident onto the transparent displayapparatus 720 on the basis of the brightness measured by theback-illuminated sensor 723 disposed on the back surface. Moreover, thetransparent display apparatus 720 is configured to secure the visibilityof the transparent display apparatus 720 by increasing the luminance ofthe displayed video depending on the brightness of the incident directlight.

When both the plurality of illuminated sensors 722 and 723 that arepositioned on the front surface and the back surface are used, thetransparent display apparatus 720 can achieve the set target contrastratio by detecting the ambient brightness environment with moreaccuracy. In addition, the transparent display apparatus 720 can provideinformativeness of the video and informativeness of the background tothe user.

Referring back to FIG. 6B, the image sensor 613 means a sensor thatobtains a two-dimensional video. Since the image sensor 613 is disposedon the back surface of the transparent display apparatus, an image onthe back surface that is capable of being seen through the transparentdisplay apparatus can be obtained.

The light transmittance determining unit 632 may determine the lighttransmittance on the basis of the obtained image. The lighttransmittance determining unit 632 may divide the obtained image into aplurality of areas, and determine the light transmittance for each ofthe divided areas.

The optical sensor 610 may include a proximity sensor 615 disposed onthe back surface of the transparent display apparatus. The proximitysensor 615 means a sensor that uses infrared rays for sensing a distanceand measures whether or not the object is in proximity to thetransparent display apparatus depending on the amount of the reflectedinfrared rays. The light transmittance control device 600 may controlthe light transmittance of the transparent display apparatus on thebasis of whether or not the object positioned on the back surface of thetransparent display apparatus is in proximity to the transparent displayapparatus. For example, when it is determined by the proximity sensor615 that the user's hand is in proximity to the transparent displayapparatus, the light transmittance is decreased by the light controlunit. Meanwhile, when it is determined that the user's hand does not isin proximity to the transparent display apparatus, the lighttransmittance is maintained, and the proximity sensor 615 may be used asan input unit for manipulating the light control unit.

FIG. 7A is a schematic diagram for describing a position of the opticalsensor 716 in the transparent display apparatus 710 according to theexemplary embodiment of the present invention. The transparent displayapparatus 710 according to the exemplary embodiment of the presentinvention includes a light-transmissive display area 712 and anon-display area 714.

In the transparent display apparatus 710 according to the exemplaryembodiment of the present invention, the position of the optical sensor716 is not limited. The optical sensor 716 may be disposed at anyposition as long as the optical sensor is disposed on one surface of thetransparent display apparatus 710 to measure light incident to theoptical sensor 716. In the transparent display apparatus 710 accordingto the exemplary embodiment of the present invention, the optical sensor716 may be disposed on the front surface, the back surface or a sidesurface of the transparent display apparatus 710. For example, when thetransparent display apparatus 710 includes a plurality of sensors, theplurality of optical sensors 716 may be independently driven, and thetransparent display apparatus 710 may recognize positional informationitems of the optical sensors 716. Specifically, the optical sensor 716is preferably disposed on the back surface. The light incident from theback surface of the transparent display apparatus 710 affects thecontrast ratio of the apparatus. In addition, since the transparentdisplay apparatus 710 maintains the target contrast ratio by controllingthe light incident from the back surface, the optical sensor 716 ispreferably disposed so as to sense the light incident from the backsurface.

In FIG. 7A, the optical sensor 716 of the transparent display apparatus710 is disposed in the non-display area 714 on one surface of thetransparent display apparatus 710. In order to measure the lightincident onto the transparent display apparatus 710 with more accuracy,the optical sensor 716 may be disposed at the center of the transparentdisplay apparatus 710.

FIG. 8 is a schematic diagram of a transparent display apparatusaccording to various exemplary embodiments of the present invention.Referring to FIG. 8, a transparent display apparatus 810 includes animage sensor 820 disposed on a back surface of the transparent displayapparatus 810. The image sensor 820 obtains an image on the back surfaceof the transparent display apparatus 810. An image 830 obtained by theimage sensor 820 is recognized and processed by the transparent displayapparatus 810. However, for the sake of convenience in description, FIG.8 illustrates that the image 830 obtained by the image sensor 820corresponds to the transparent display apparatus 810.

The transparent display apparatus 810 may analyze the obtained image 830and divide the image into a plurality of areas L1, L2 and L3. Theobtained image 830 includes the plurality of areas L1, L2 and L3, andthe plurality of areas has different brightness values. For example, thearea L1 may have the smallest brightness value, the area L2 may have anaverage brightness value, and the area L3 may have the largestbrightness value. Arrows depicted in the areas L1, L2 and L3 representrelative brightness values. The transparent display apparatus 810according to the present invention controls the light transmittance ofareas of the transparent display apparatus 810 corresponding to thedivided areas of the obtained image 830. Referring to FIG. 8, thetransparent display apparatus may determine the light transmittance suchthat the area of the transparent display apparatus 810 corresponding tothe area L1 has the maximum light transmittance, the area of thetransparent display apparatus 810 corresponding to the area L2 has themiddle light transmittance, and the area corresponding to the area L3has the minimum light transmittance.

Further, the transparent display apparatus 810 obtains a plurality ofimages having time lags from the image sensor 820, compares the obtainedplurality of images with each other, and detects that the transparentdisplay apparatus 810 is moving or a position of the transparent displayapparatus 810 is changed. When a change in position of the transparentdisplay apparatus 810 is detected, the transparent display apparatus 810can adjust the light transmittance to ensure the visibility.

When the light transmittance is controlled by measuring the lightcharacteristics by the image sensor 820, a distribution of the lightincident onto one image sensor 820 is predicted without using theplurality of illuminated sensors. Furthermore, although it has beenexplained in FIG. 8 that the distribution of the light is measured bythe image sensor 820, the distribution of the light may be measured byother optical sensors.

FIGS. 9A and 9B are schematic diagrams of a transparent displayapparatus according to various exemplary embodiments of the presentinvention.

Referring to FIG. 9A, a transparent display apparatus 910 includes aproximity sensor 912 disposed on a back surface of the transparentdisplay apparatus 910. The proximity sensor 912 includes a lightemitting part and a light receiving part. The proximity sensor 912 meansa sensor that uses infrared rays for sensing a distance or whether ornot the object is in proximity to the sensor and measures the distanceor whether or not the object is in proximity to the sensor depending onthe amount of the reflected infrared rays. The light emitting part ofthe proximity sensor 912 emits light in one direction. The light reachesan object 916, is reflected from the object, and then enters the lightreceiving part of the proximity sensor 912. The light receiving part maycompare the measured amount of light and the amount of emitted light andmeasure whether the object is positioned within a distance between theproximity sensor 912 and the object 916 or a predetermined proximitydistance. The transparent display apparatus 910 controls the lighttransmittance of the transparent display apparatus 910 on the basis ofwhether or not the object 916 is in proximity to the back surface of thetransparent display apparatus 910.

The proximity sensor 912 of FIG. 9A measures a distance of the object916, and FIG. 9A illustrates that the distance between the transparentdisplay apparatus 910 and the object 916 is within a certain distance.For example, when the transparent display apparatus 910 determines thatthe object 916 on the back surface of the transparent display apparatus910 is positioned within the certain distance using the proximity sensor912 including the light emitting part and the light receiving part, thetransparent display apparatus can increase the light transmittance byadjusting the light transmittance of the light control unit.

Referring to FIG. 9B, the proximity sensor 912 of a transparent displayapparatus 920 measures the distance of the object, and FIG. 9Billustrates that a distance between the transparent display apparatus920 and an object 926 is outside a certain distance. For example, whenthe transparent display apparatus 920 determines that the object 926 onthe back surface of the transparent display apparatus 920 is positionedwithin the certain distance using the proximity sensor 912 including thelight emitting part and the light receiving part, the transparentdisplay apparatus can decrease or increase the light transmittance byadjusting the light transmittance of the light control unit.

The proximity sensor 912 illustrated in FIGS. 9A and 9B may be used incombination with the optical sensor that measures characteristics ofdifferent light rays. For example, the proximity sensor 912 may be usedby being connected to the illuminated sensor that measures thebrightness. For example, when the a smart phone device including thetransparent display apparatus is placed on a table, when the illuminatedsensor measures low brightness and the proximity sensor detects highproximity, the light transmittance of the transparent display apparatusmay be determined to be decreased. Even under the same brightness level,the transparent display apparatuses 910 and 920 may determine lighttransmittance values such that a light transmittance value when theobject 916 or 926 presumed to be a light source is farther from thetransparent display apparatus and a light transmittance value when theobject is close to the transparent display apparatus are different fromeach other.

FIG. 10 is a graph for describing a change of shielding rate and ameasured value of the optical sensor of the present invention.Characteristics of the light measured by the optical sensor in thetransparent display apparatus according to the exemplary embodiment ofthe present invention are varied with time. The transparent displayapparatus according to the exemplary embodiment of the present inventionmay set the transmittance or shielding rate of the transparent displayapparatus to a constant predetermined level for a second time when themeasured light characteristics are continuously varied, that is, when apredetermined number of variable frequencies are detected for a firstpredetermined period of time. The transparent display apparatuspreferably maintains the shielding rate at a high level. Hereinafter, anoperation of the transparent display apparatus according to theexemplary embodiment of the present invention that is operated tocorrespond to a rapid change in the brightness environment is described.

Referring to FIG. 10, an x-axis is an axis of time, and a y-axis is anaxis of a light shielding rate of the light control unit and brightnessmeasured by the optical sensor. The graph illustrates zones A, B, C andD divided for each measured time. A solid line graph of the measuredbrightness may be measured brightness of light incident on the backsurface of the transparent display apparatus according to the exemplaryembodiment of the present invention. A dotted line graph may beshielding rate of the light incident on the back surface in thetransparent display apparatus according to the exemplary embodiment ofthe present invention.

In the zone A, the measured brightness is maintained at low and theshielding rate is constantly maintained to correspond to the measuredbrightness. As the measured brightness is rapidly increased at a starttime of the zone B, the shielding rate is increased to ensure thevisibility of the video. As the measured brightness is decreased at anending time of the zone B, the shielding rate is decreased. However,immediately after the zone B where the measured brightness is varied isfinished, the measured brightness is rapidly increased at a startingtime of the zone C, and the measured brightness is continuously variedin the zone C. When the shielding rate is continuously varied along witha variation in the measured brightness, it may be difficult to maintainthe visibility of the displayed video. Accordingly, when the measuredbrightness is continuously varied for the first time (e.g., at start ofzone C), the transparent display apparatus according to the exemplaryembodiment of the present invention can maintain the visibility of thevideo even though the brightness environment is rapidly changed byincreasing and maintaining the shielding rate of the transparent displayapparatus for the second time (e.g., at end of zone C).

In FIG. 10, although it has been illustrated that the measured lightcharacteristics are the brightness of the light incident on the backsurface, the light characteristics that can be measured by thetransparent display apparatus according to the exemplary embodiment ofthe present invention are not limited. The light characteristics may bea distance between the back surface and the object, and the brightnessof the light incident on the front surface in addition to thebrightness.

FIG. 11 is a flowchart illustrating a method for controlling atransparent display apparatus according to an exemplary embodiment ofthe present invention. For the sake of convenience in description, themethod for controlling a transparent display apparatus is described withreference to the optical sensor, the transparent display and the opticalcontrol unit of the transparent display apparatus. Further, all stepsmay be independently performed, but are described as one procedure inthe following description for the sake of convenience in description.

The optical sensor of the transparent display apparatus measurescharacteristics of incident light (S100). The characteristics ofincident light are converted into analog electric signals by the opticalsensor, and the converted analog signals are converted into digitalsignals by the ADC converter. The converted digital signals are input tothe processing unit. The optical sensor may be an optical sensor formeasuring brightness of light, a distribution of light, and a distancefrom the object on the back surface. A direction of the light may bemeasured depending on the position of the optical sensor.

The processing unit determines light transmittance of the transparentdisplay apparatus on the basis of the measured characteristics of light(S110). The processing unit may determine the light transmittance so asto improve the visibility of the transparent display apparatus dependingon the light characteristics. The transparent display apparatus maydetermine the light transmittance so as to achieve the target contrastratio, or may determine the light transmittance so as to be approximateto the target brightness environment.

The transparent display apparatus controls the light control unit torealize the determined light transmittance (S120). In order to realizethe determined light transmittance, the black charged particles that canchange the characteristics of the light are moved by an electric fieldand the black charged particles are collected or spread, so that thelight control unit can transmit or shield the incident light.

FIG. 12 shows schematic diagrams of apparatuses to which the transparentdisplay apparatus according to the exemplary embodiment of the presentinvention is applicable.

(a) of FIG. 12 illustrates a case where the transparent displayapparatus according to the exemplary embodiment of the present inventionis attached to a transparent device 3100. The transparent device 3100may include a transparent display apparatus 3110, a control unit 3120and an input unit 3130. The transparent display apparatus 3110 may beformed such that no bezel is formed on at least one surface of thetransparent display apparatus 3110 or the minimum number of bezels isformed on the at least one surface thereof. The transparent device 3100may include an application for utilizing an augmented reality functionthrough the transparent display apparatus 3110 or other functions of thetransparent display apparatus 3110 by the control unit 3120. Thetransparent device 3100 may select various modes for controlling thetransparent display apparatus 3110 by using a separate input unit 3130such as buttons. The modes for controlling the transparent displayapparatus 3110 may include a transmissive mode, a shield mode, an e-bookmode, and light-transmittance automatic control mode. The separate inputunit 3130 may be used when the visibility of the transparent displayapparatus 3110 is rapidly deranged by the ambient brightness environmentand it is difficult to select a control window displayed on thetransparent display apparatus 3110.

(b) of FIG. 12 illustrates a case where the transparent displayapparatus according to the various exemplary embodiment of the presentinvention is used as a transparent device 3200 or a display apparatus ofa screen. The transparent device 3200 may be configured to recognize avideo through the transparent display apparatus 3210 and an object on aback surface of the transparent display apparatus 3210, or may beconfigured to be utilized as a double-sided display. That is, thetransparent display apparatus 3210 according to the exemplary embodimentof the present invention may be used by being attached to anotherdisplay apparatus.

In this case, a design of the transparent display apparatus may bepartially changed depending on a kind of another display apparatus. Forexample, when another display apparatus is a transparent organiclight-emitting display apparatus, in order for the transparent displayapparatus 3210 to be a double-sided display apparatus, the transparentdisplay apparatus 3210 may configured to allow a plurality of videos tobe input. Further, when the double-sided display apparatus is driven,the transparent display apparatus may be driven to be operated in theshield mode in which the light control unit shields the incident light.The transparent device 3200 may be configured to display a controlwindow 3220 capable of selecting various modes for controlling thetransparent display apparatus 3210. The modes for controlling thetransparent display apparatus 3210 may include a transmissive mode, ashield mode, an e-book mode, and light-transmittance automatic controlmode. The user can accomplish the purpose of using the transparentdisplay apparatus 3210 by appropriately selecting the mode forcontrolling the transparent display apparatus 3210.

(c) of FIG. 12 illustrates a case where the transparent displayapparatus according to the various exemplary embodiment of the presentinvention is used as a display apparatus of a transparent mobile device3300. (c) of FIG. 12 illustrates that a transparent display apparatus3310 according to the various exemplary embodiment of the presentinvention is included in the transparent mobile device 3300, but thetransparent display apparatus may be provided at a mobile device or asmall-sized device such as a smart phone, a cellular phone, a tablet PC,a PDA. When the transparent display apparatus is provided at thesmall-sized device, since a built-in battery is used without using anexternal power supply, the elements of the transparent display apparatus3310 may be designed to be suitable for the limited capacity of thebattery. When the transparent display apparatus 3310 is used as thedisplay apparatus of the transparent mobile device 3300, the transparentdisplay apparatus may include a touch-screen for user input of thetransparent mobile device 3300. The touch-screen may be formed on thetransparent display apparatus 3310, or may be formed in in-cell type.Further, since the back surface of the transparent display apparatus3310 can be recognized, the touch-screen may be configured to sensetouch of both sides of the transparent display apparatus 3310.Furthermore, the mobile device 3300 may include a proximity sensor, andthe operation of the mobile device may be changed depending on whetheror not the user or the object approaches or the approaching degree.

(d) of FIG. 12 illustrates a case where the transparent displayapparatus according to the various exemplary embodiment of the presentinvention is used as a display apparatus of smart glasses 3400. Thesmart glasses 3400 include a transparent display apparatus 3410 and acontrol unit 3420. When the transparent display apparatus 3410 accordingto the various exemplary embodiment of the present invention is used inthe smart glasses 3400, the transparent display apparatus may be cut offin a rectangular shape or an ellipse shape, and a wiring suitable forvarious shapes and a driving unit may be set in the transparent displayapparatus. Moreover, since a viewing side of the user becomes close tothe transparent display apparatus 3410, an optical coating process maybe appropriately performed on the transparent display apparatus 3410, ora driving resolution of the video may be appropriately selected.

(e) of FIG. 12 illustrates a case where the transparent displayapparatus according to the various exemplary embodiment of the presentinvention is included in a refrigerator 3500. A transparent displayapparatus 3510 may be used as a part of a door 3520 of the refrigerator.When the transparent display apparatus 3510 is used as the door 3520 ofthe refrigerator, the transparent display apparatus 3510 may include adevice that reflects energy other than a device that absorbs light orenergy. For example, white charged particles other than the blackcharged particles may be used as the particle charged of the lightcontrol unit of the transparent display apparatus 3510. In addition, inorder to easily see an object within the refrigerator 3500 on a backsurface of the transparent display apparatus 3510, a dehumidificationcoating process may be performed on the transparent display apparatus3510.

(f) of FIG. 12 illustrates a case where the transparent displayapparatus according to the various exemplary embodiment of the presentinvention is used as an advertisement displaying apparatus 3600 of a busstation. (f) of FIG. 12 illustrates that a transparent display apparatus3610 according to the various exemplary embodiment of the presentinvention is included in the advertisement displaying apparatus 3600 ofa bus station, but the transparent display apparatus may be provided ata fixation device or a large-sized device such as a television or abillboard. Since a power is supplied from an external power supply, theelements of the thin-film transistor may be designed so as to realizehigher definition of the transparent display apparatus 3610 due to astabilized power supply. Further, the advertisement displaying apparatusof a bus station may include a motion sensor capable of interacting withpedestrians. For example, the motion sensor may include TOF (Time ofFlight) infrared sensor.

When the transparent display apparatus according to the variousexemplary embodiment of the present invention is used as a smart window,the transparent display apparatus may include a supporting member forusing as at least the smart window, and the supporting member mayinclude all kinds of films such as a film and a protection film that canbe used in the smart window. Moreover, a design of the transparentdisplay apparatus may be partially changed depending on a place in whichthe smart window is provided. For example, when the transparent displayapparatus is provided at a high-humidity place such as a toilet, abasin, a shower room, or a kitchen, the light control unit may bedesigned using moisture-resistance elements.

In addition, when the smart window is provided at a place that is easilyexposed to external impact, such as an external wall of a building, awindow glass of a building or a window glass of a vehicle, thetransparent display apparatus may be designed using elements that easilyabsorb impact or have impact resistance.

Further, when the transparent display apparatus is used as the smartwindow, various optical films for reinforcing optical and/or physicalcharacteristics may be attached to the transparent display apparatus. Areflecting film, a diffusing film, a prism film, a lens-patterncomposite film, a double brightness enhancement film, a non-reflectingcoat film, an anti-ultraviolet film, or an anti-infrared film may usedto reinforce optical and/or physical characteristics. The smart windowto which the transparent display apparatus is attached depending on thereinforced characteristics may be used as a window for a vehicle, asmart door, a projection wall, or a smart mirror.

The components of various embodiments of the present invention can bepartially or entirely bonded to or combined with each other and can beinterlocked and operated in technically various ways as can be fullyunderstood by an ordinary person skilled in the art, and the embodimentscan be carried out independently of or in association with each other.

Combinations of each block of the accompanying block diagram and eachstep of the flow chart can be implemented by algorithms or computerprogram instructions comprised of firmware, software, or hardware. Sincethese algorithms or computer program instructions can be installed inprocessor of a universal computer, a special computer or otherprogrammable data processing equipment, the instructions executedthrough a processor of a computer or other programmable data processingequipment generates means for implementing functions described in eachblock of the block diagram or each step of the flow chart. Since thealgorithms or computer program instructions can be stored in a computeravailable or computer readable memory capable of orienting a computer orother programmable data processing equipment to implement functions in aspecific scheme, the instructions stored in the computer available orcomputer readable memory can produce items involving an instructionmeans executing functions described in each block of the block diagramor each step of the flow chart. Since the computer program instructionscan be installed in a computer or other programmable data processingequipment, a series of operation steps are carried out in the computeror other programmable data processing equipment to create a processexecuted by the computer such that instructions implementing thecomputer or other programmable data processing equipment can providesteps for implementing functions described in functions described ineach block of the block diagram or each step of the flow chart.

Further, each block or each step may indicate a part of a module, asegment, or a code including one or more executable instructions forimplementing specific logical function(s). Furthermore, it should benoted that in some alternative embodiments, functions described inblocks or steps can be generated out of the order. For example, twoblocks or steps illustrated continuously may be implementedsimultaneously, or the blocks or steps may be implemented in reverseorder according to corresponding functions.

The steps of a method or algorithm described in connection with theembodiments disclosed in the present specification may be embodieddirectly in hardware, in a software module executed by a processor, orin a combination of the two. The software module may reside in RAMmemory, flash memory, ROM memory, EPROM memory, EEPROM memory, register,hard disk, a removable disk, a CD-ROM, or any other form of storagemedium known in the art. An exemplary storage medium is coupled to theprocessor such that the processor can read information from, and writeinformation to, the storage medium. Otherwise, the storage medium may beintegrated with the processor. The processor and the storage medium mayreside in an application-specific integrated circuit (ASIC). The ASICmay reside in a user terminal. Otherwise, the processor and the storagemedium may reside as discrete components in a user terminal.

The exemplary embodiments of the present invention have been describedin more detail with reference to the accompanying drawings, but thepresent invention is not limited to the exemplary embodiments. It willbe apparent to those skilled in the art that various modifications canbe made without departing from the technical sprit of the invention.Accordingly, the exemplary embodiments disclosed in the presentinvention are used not to limit but to describe the technical spirit ofthe present invention, and the technical spirit of the present inventionis not limited to the exemplary embodiments. Therefore, the exemplaryembodiments described above are considered in all respects to beillustrative and not restrictive. The protection scope of the presentinvention must be interpreted by the appended claims and it should beinterpreted that all technical spirits within a scope equivalent theretoare included in the appended claims of the present invention.

What is claimed is:
 1. A transparent display apparatus, comprising: atransparent display unit having light emitting pixel elements andtransmitting at least a portion of first light incident on thetransparent display apparatus; and at least one sensor to generate atleast one signal indicative of brightness of second light incident onthe transparent display apparatus, wherein the portion of the firstlight transmitted through the transparent display unit is adjustablebased on the signal indicative of the brightness of the second light. 2.The transparent display apparatus of claim 1, wherein the first light isthe second light.
 3. The transparent display apparatus of claim 1,wherein the first light and the second light are incident on oppositesurfaces of the transparent display apparatus.
 4. The transparentdisplay apparatus of claim 1, further comprising: a light control unitoverlapping with the transparent display unit, the light control unithaving an adjustable transmittance for the first light, wherein theamount of the portion of the first light transmitted through thetransparent display unit is adjustable by adjusting the adjustabletransmittance of the light control unit based on the signal indicativeof the brightness of the second light.
 5. The transparent displayapparatus of claim 4, wherein the at least one sensor comprises aplurality of sensors that generate a plurality of signals indicative ofthe brightness of the second light at different positions of thetransparent display apparatus, and wherein the adjustable transmittanceof the light control unit is adjustable in different areas correspondingto the different positions of the transparent display apparatus based onthe plurality of signals.
 6. The transparent display apparatus of claim1, wherein the at least one sensor also measures a proximity between thetransparent display apparatus and an external object, and wherein theportion of the first light transmitted through the transparent displayunit is further adjustable based on the proximity.
 7. The transparentdisplay apparatus of claim 1, wherein the at least one sensor comprisesan image sensor.
 8. The transparent display apparatus of claim 1,wherein the portion of the first light transmitted through thetransparent display unit is further adjustable based on a targetcontrast ratio of the transparent display apparatus.
 9. The transparentdisplay apparatus of claim 1, wherein the portion of the first lighttransmitted through the transparent display unit is further adjustablebased on a maximum luminance of the light emitting pixel elements. 10.The transparent display apparatus of claim 1, wherein the portion of thefirst light transmitted through the transparent display unit isdecreased as the brightness of the second light increases.
 11. Thetransparent display apparatus of claim 1, wherein the transparentdisplay apparatus supports a first mode, a second mode and a third mode,wherein: in the first mode, the portion of the first light transmittedthrough the transparent display unit is maximized, in the second mode,the portion of the first light transmitted through the transparentdisplay unit is minimized, and in the third mode, the portion of thefirst light transmitted through the transparent display unit isadjustable based on the signal indicative of the brightness of thesecond light.
 12. The transparent display apparatus of claim 1, whereinthe portion of the first light transmitted through the transparentdisplay unit is maintained constant when the brightness of the secondlight changes more than a predetermined number of times in apredetermined period.
 13. A method of operation in a transparent displayapparatus that includes a transparent display unit having light emittingpixel elements and transmitting at least a portion of external lightincident on the transparent display apparatus, the method comprising:generating at least one signal indicative of brightness of the externallight incident on the transparent display apparatus; and adjusting theportion of the external light transmitted through the transparentdisplay unit based on the signal indicative of the brightness of theexternal light.
 14. The method of claim 13, wherein the portion of theexternal light transmitted through the transparent display unitdecreases as the brightness of the external light increases.
 15. Themethod of claim 13, wherein the transparent display apparatus comprisesa light control unit overlapping with the transparent display unit, thelight control unit having an adjustable transmittance for the externallight, and wherein adjusting the portion of the external lighttransmitted through the transparent display unit comprises: adjustingthe adjustable transmittance of the light control unit based on thesignal indicative of the brightness of the external light.
 16. Themethod of claim 15, wherein the portion of the external lighttransmitted through the transparent display unit is further adjustedbased on a target contrast ratio of the transparent display apparatus.17. A computer readable medium storing instructions for operation of atransparent display apparatus that includes a transparent display unithaving light emitting pixel elements and transmitting at least a portionof external light incident on the transparent display apparatus, theinstructions when executed by a processor cause the processor to performa method comprising: generating at least one signal indicative ofbrightness of the external light incident on the transparent displayapparatus; and adjusting the portion of the external light transmittedthrough the transparent display unit based on the signal indicative ofthe brightness of the external light.